[#21] Add C++23 standard badge and update requirements in README

[hazareajinkya]

Description

This PR addresses Issue #21: The README was missing the C++ version/standard.

Changes

• Added a C++23 badge ([![C++23](https://img.shields.io/badge/C%2B%2B-23-blue.svg)]) alongside existing badges at the top of the README
• Updated the project description to mention C++23 explicitly: "C++ Trader is a set of components written in C++23 for building high performance Trading Platform"
• Added "C++23 Standard Compiler" to the Requirements section

Rationale

The project uses CMAKE_CXX_STANDARD 23 in its CMake configuration (via CppCMakeScripts's SetCompilerFeatures.cmake), making it clear that C++23 standards features are available and expected. This information should be surfaced in the README for developers.

Verification

• The C++23 standard is confirmed in the cmake scripts: set(CMAKE_CXX_STANDARD 23)